Carrier concentration ratio and Hall mobility of semi−insulating GaAs upon photoexcitation and electron bombardment

The electron−hole concentration ratio (c) and the Hall mobility (μH) of Cr−doped semi−insulating p−type GaAs crystals were investigated as a function of illumination intensity (I), before and after bombardment with 90Sr−90Y β− particles. The quantities c and μH were determined by using photomagnetoresistance and photo−Hall measurements at room temperature. The ratio c as a function of I shows a minimum due to the action of traps. Bombardment with β− particles introduces new trapping levels resulting in a marked change of the ordinate of the minimum.